Container Sealing Machine for Food Packaging

ABSTRACT

A sealing machine for a fresh-keeping and cooking container is provided. The sealing machine includes a lidding-film processing unit, a bonding unit, and a heat-sealing unit. The lidding-film processing unit includes die cutters and hot needles for forming line-segment-shaped, spaced slits and dot-shaped atmosphere-modifying breathing holes on a surface of a lidding film passing through the lidding-film processing unit. The processed lidding film then enters the bonding unit and is bonded with an airtight sealing strip whose bottom is provided with adhesive. Afterward, the lidding film bonded with the sealing strip enters the heat-sealing unit so as to cover an opening of a container and be heat-sealed to a heat-sealable rim of the opening. Thus, the lidding film is processed and sealed to the container in a continuous manner to simplify sealing of the container and removal of scraps cut from the used lidding film.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a sealing machine for sealing a foodcontainer and enabling the sealed container to preserve the freshness offood contained therein in a modified atmosphere and to automaticallyregulate the build up steam pressure generated during microwave heating.More particularly, the present invention relates to a sealing machinewhich provides a continuous process of processing a lidding film,filling frozen or refrigerated food into a container, and then sealingopening of the container with the processed lidding film.

2. Description of Related Art

A conventional sealing machine for sealing frozen or refrigerated foodis typically configured to work in the following manner. A roll ofpre-fabricated lidding film is provided from a roll stock film unwindingset of the sealing machine. Meanwhile, a container filled with food tobe frozen or refrigerated is in place at a sealing position of thesealing machine. When the sealing machine is started, the lidding filmis unwound and extended downward from the roll of lidding film at theend of the sealing machine so as to pass over the container. The liddingfilm covering the container is hot-pressed and thus sealed to an openingof the container by a sealing mechanism. After the sealing process,scraps die cut from the edge of lidding film are wound up to a rewindingspool located at an opposite end of the sealing machine. Thus, theopening of the container containing the to-be-frozen orto-be-refrigerated food is sealed.

In the early days, a commonly used technique to preserve the freshnessand quality of fruits and vegetables is to lower the temperature of theStorage environment. In a low-temperature environment, living fruits andvegetables have a reduced metabolic rate, and in consequence theoxidation and consumption of organic sugar, starch, and fat in thefruits and vegetables slow down, which delays the ripening and yellowingof the fruits and vegetables. In addition, it was found decades ago thatthe metabolic rate of fresh fruits and vegetables can also be decreased,and their shelf life increased, by adjusting oxygen and carbon dioxideconcentrations in the packaging area surrounding the fruits andvegetables. In fact, the modified-atmosphere packaging (MAP) techniqueis an application based on and integrated with the refrigerationtechnique so as to enhance the effect of freshness prolongation onfruits and vegetables by both refrigeration and atmosphere modification.During the past few decades, studies on freshness preservation, storage,and transportation in a modified atmosphere packaging have thrived.Since different fruits and vegetables have different structurecharacteristic, the outer surface area of a leafy vegetable that is incontact with air and available for breathing differs from that of afresh vegetables with a stem or root tuber. A leafy vegetable also has adifferent metabolic respiration rate from a stem or root tuber.Likewise, total oxygen demand and carbon dioxide emission vary from onespecies to another. Generally speaking, leafy vegetables have relativelylarge surface areas, require a relatively larger amount of air formetabolic respiration, and consequently ripen and yellow relativelyfaster. In order to slow down metabolic respiration, themodified-atmosphere packaging technique requires that storagetemperature and oxygen concentration be low, and carbon dioxideconcentration be high. By contrast, a fresh vegetable with stem or roottubers, which breathe only through their outer skin, have lower oxygendemand, are less sensitive to the change of oxygen concentration in theenvironment, and therefore have higher tolerance to variations intemperature and oxygen and carbon dioxide concentrations during storageand transportation. The atmospheric environment contains approximately20.9% of oxygen and 0.03% of carbon dioxide. If fresh fruits andvegetables are stored in an environment whose temperature is adjusted toa refrigeration temperature of 0° C. to 5° C., whose oxygenconcentration is lowered to 2% to 15%, and whose carbon dioxideconcentration is raised to 5% to 30%, the shelf life of the fruits andvegetables can be extended significantly from three days to more thanten days, which is helpful to long-term storage and long-distancetransportation and distribution of fruits and vegetables in continentalcountries. For produce grower in areas of capricious weather conditionsand having high requirements for freshness and quality, the developmentof packaging materials for use in modified-atmosphere packagingapplication is important. Hence, many countries have put great effortsinto the research and development of special packaging materials forfruits and vegetables. Presently, freshness preservation techniques forfruits and vegetables can be divided into two major categories, namelycontrolled-atmosphere packaging (CAP) and modified-atmosphere packaging(MAP). In controlled-atmosphere packaging, the various gasconcentrations in a packaged atmosphere are under an active controllablemethod. More specifically, oxygen and carbon dioxide concentrations inthe packaged atmosphere are regulated and kept constant by means ofdetection equipment and external supply of oxygen and carbon dioxide.Therefore, fruits and vegetables stored in such a packaged atmospherehave their respiration and metabolic rates lowered in exchange forextended shelf life and high quality. However, the control system,including hardware and software, for controlled-atmosphere packaging iscostly. On the other hand, modified-atmosphere packaging is carried outby packaging fresh fruits and vegetables with a special air-permeablepackaging material such that, due to metabolism and respiration of thefruits and vegetables under a specific storage temperature, coupled withthe special gas permeability of the packaging material, oxygen andcarbon dioxide concentrations in the packaged atmosphere gradually reacha dynamic equilibrium state and thus meet the required fresh-keepingconditions. The cost of modified-atmosphere packaging is lower than thatof controlled-atmosphere packaging.

While the shelf life of fresh fruits and vegetables can be extended byapplying the hardware, software, and packaging materials of theaforesaid two packaging techniques, neither of these packagingtechniques provides the dual function of the packaging materialdisclosed in the present invention, namely atmosphere modification forfreshness preservation and automatic regulating the build up hot steampressure when the packaged fruits and vegetables are directly heated bymicrowave. Generally, a packaging material for preserving the freshnessof fruits and vegetables in a modified atmosphere has an oxygenpermeability ranging approximately from 20 to 200000 cc/(day·m²·atm·25°C.). However, the overall air-regulating capacity of such a packagingmaterial for modified-atmosphere freshness preservation is not enough toregulate the huge instantaneous amount of build up hot steam generatedwhen the packaged fruits and vegetables are heated by microwaveespecially at the onset of boiling temperature; the packaging materialwill burst and break when subjected to such vast vapor. Polyethylene orpolypropylene bags with a thinner gauge made by their blown films arecommon packaging materials for fruits and vegetables and havefresh-keeping and air-permeable properties. These bags, though capableof modified-atmosphere freshness preservation, are not suitable for useas closed packages microwave heating because the bags cannot regulateand withstand the vast amount of build up hot steam pressure generatedinstantly upon microwave heating.

Fresh fruits and vegetables sealed in a closed container for storage andtransportation are basically living plants. When oxygen in the containeris continuous depletion, and carbon dioxide concentration becomes toohigh, the fruits and vegetables sealed in the container begin to rot,yellow, and produce unpleasant odor. In order to prevent fruits andvegetables from rotting due to lack of oxygen, the container is usuallyperforated by die cutting so as to enable rapid exchange of oxygenbetween the interior of the container and ambient atmosphere, thusallowing the living fruits and vegetables to survive. When massive gasexchange takes place, however, oxygen and carbon dioxide concentrationsinside and outside the container become virtually equal, namely 20.9% ofoxygen and 0.03% of carbon dioxide. Now that the fruits and vegetablesare stored substantially in an atmospheric environment and are allowedto restore their normal respiration and metabolic rates, the containerhas lost the ability to significantly extend the shelf life of itscontent.

Nowadays, modified-atmosphere freshness preservation of fruits andvegetables is mostly implemented via an air-permeable mixed polymermaterial. The material is formed into an air-permeable film byco-extrusion, film blowing, or a T-die stretching technique. In additionto complexity of the manufacturing process, the resultant film is alsodisadvantaged by the fact that its oxygen permeability and carbondioxide permeability are not applicable to the modified-atmospherepreservation of all fruits and vegetables. More importantly, theresultant air-permeable film cannot be used to regulate the large amountof high-temperature, high-pressure vapor generated in a closedmicrowave-heated environment. There are many breathable packagingmaterials on the market that have special air-permeability for thepreservation of fruits and vegetables but are not suitable for use in aclosed microwave-heated environment. A few examples of thesecommercially available air permeable packaging materials and theirmanufacturing technologies are described as follows.

1. A plastic material is blended and thoroughly mixed with an inorganicpowder. The blended mixture goes through a blowing or T-die extrusionprocess and is stretched by a mono or two directional stretching tenterso as to form an air-permeable film. For instance, an inorganic powderof calcium carbonate (CaCO₃), titanium dioxide (TiO₂), or aluminum oxide(Al₂O₃) is evenly mixed with an organic polymer material such aspolyethylene, prior to being extruded into a film. Similar techniquesare disclosed in U.S. Pat. Nos. 3,679,540; 4,187,390; 4,350,655;4,466,931; 4,777,073; and 5,340,646. While the resultant film hasspecial air-permeability and meets the requirements formodified-atmosphere packaging, it generally does not qualify for use ina closed package that is to be directly heated by microwave, for thefollowing reasons: 1) The film has not enough mechanical strength. 2)The film has a low melting point. The material commonly used for makingthe film is polyethylene or polypropylene, both of which have lowmelting points. When mixed with a higher percentage of inorganic powder,the elongation ratio of this higher weight percentage of blendedinorganic powder is limited. In practice, with a higher solid content,the stretched film tends to break during the stretching process, and theinorganic powder may fall off easily. 3) The formula of the film oftenincludes additives such as a lubricant. The added lubricant or theaforesaid inorganic powder may migrate to or contact with food duringmicrowave cooking and cause an undesirable effect on the human body.Furthermore, the lubricant additive, such as wax, may produce unpleasantodor during microwave heating. In short, the low mechanical strength andlow melting point prevent the film from being used in a closed packagethat is directly heated by microwave. Besides, due to not enough steampressure regulating ability, the film tends to extend excessively oreven rupture when subjected to continuous heating and huge instantaneousbuild up steam pressure.

2. A plastic resin material is blended with an additive having a lowmolecular weight, such as mineral oil. After the film is formed, themineral oil is extracted by a special solvent. More specifically, theplastic material is evenly mixed with the mineral oil. Then, the mixtureis converted into a film via a T-die or through a film casting process.Furthermore, the mineral oil is extracted and thus removed by thesolvent, so as to produce an air-permeable film. The principle of theforegoing manufacturing process is to make a film having a porousstructure out of a mixture of incompatible materials and then remove acertain ingredient by solvent extraction. Similar techniques aredisclosed in U.S. Pat. Nos. 3,378,507; 3,310,505; 3,607,793; 3,812,224;4,247,498; 4,466,931; and 5,928,582. While a film thus formed hasspecial air-permeability and meets the requirements formodified-atmosphere packaging, it is generally incapable of regulatingthe large amount of high temperature, hot steam pressure generated in aclosed microwave-heated package and may rupture as a result. Moreover,considerations must be made for the risk of having residual mineral oilin contact with food, as well as for the excessive extension and burstof the film under continuous high temperature.

3. Another air-permeable material, as taught by U.S. Pat. No. 5,865,926,is made of an air-permeable non-woven fabric or fibrous web. However, anair-permeable film produced by such a method has a macroporous structureand is unsatisfactory in terms of food packaging, taste, flavorpreservation, and efficient use of energy.

The packaging materials described above are capable ofmodified-atmosphere freshness preservation but incapable ofautomatically regulating the build up hot steam pressure generatedduring microwave heating. To prevent the packaging materials frombursting fracture due to the instantaneous huge build up hot steam andpressure during microwave heating or other cooking means, it is commonpractice to form pressure-releasing macro holes in the packagingmaterials or trays by laser microperforation or machine die cutting.Air-permeable packaging materials with macro holes, whose diameters areoften greater than 1 mm, can not be used in a closed microwave-heatedenvironment but, owing to their high air-permeability, turn out to behigh-permeable packaging materials, which may lead to dehydration of thepackaged food. In practice, these macro-hole packaging materials fail toprolong the shelf life of fresh fruits and vegetables. In addition, apackaging material for fruits and vegetables that is perforated by diecutting tends to have a air-permeability so high that not only are thevarious gas concentrations around the packaged fruits and vegetablessubstantially the same as those in the ambient atmosphere, but alsosmall insects and fungi are allowed easy access through the holes.Furthermore, in case of overtime microwave cooking, the macro holes maycause the food to lose excessive moisture during the heating process andend up dry and hard.

Although the foregoing air-permeable packaging materials and theirmanufacturing methods are well known in the art, those packagingmaterials do not serve the dual function of modified-atmospherefreshness preservation and proper pressure regulation in a closedmicrowave-heated environment. More importantly, those packagingmaterials have a relative high production costs.

BRIEF SUMMARY OF THE INVENTION

The inventor of the present invention has endeavored to improvemicrowavable food-packaging materials and their production processes.The present invention relates to the integration of a sealing machineand a container for storing frozen or refrigerated fresh or cooked food,thereby enabling the container to preserve the freshness of its contentand be directly heated by microwave. The subject matter of the presentinvention has never been disclosed in the above-cited prior art.

The present invention provides a novel design of a sealing machineconfigured for sealing a container which contains food to be frozen orrefrigerated. According to the present invention, a lidding film forcovering an opening of a container is processed and then sealed to thecontainer in a continuous fashion so as to simplify sealing of thecontainer and removal of scraps cut from the used lidding film.Heat-sealing the lidding film to a loaded food container may have thefollowing functional appeals: 1) Frozen or refrigerated food can becompletely sealed to prevent ice burn which may otherwise result fromprolonged frozen storage. Besides, the food can be directly heated bymicrowave oven in the frozen state and serve when cooked. 2) Freshfruits and vegetables can be refrigerated and kept fresh in a modifiedatmosphere packaging for storage and transportation. The fruits andvegetables can also be directly heated by microwave oven and serve whencooked. 3) Fresh fruits and vegetables, such as fresh-cut produce whichhas been washed, packaged, and vacuum pre-cooled, can stay fresh underrefrigeration and be eaten directly. There is no need to open thelidding or to cut a hole to the lidding prior to microwave heating toprevent the bursting fracture.

The present invention provides a sealing machine for rendering a foodcontainer capable of modified-atmosphere freshness preservation as wellas automatic build up vast hot steam pressure regulation duringmicrowave heating. The sealing machine includes hot needles configuredfor quantitatively controlling the diameter and number of melted holesformed in a lidding film sealed to the container. Consequently, theair-permeable composite lidding film has a specific gas permeationcapacity and is applicable to fresh fruits and vegetables of differentkinds and different weights for extending their shelf life of freshness.

On the other hand, the lidding film is formed with line-segment-shaped,spaced slits and provided with an airtight sealing strip such that thecontainer is completely air tight during storage and transportation butcan rapidly regulate the large amount of high-temperature, high-pressurehot steam generated instantly during microwave cooking, therebypreventing the container from bursting. The amount of vapor that theline-segment-shaped, spaced slits are capable of regulating is fargreater than the small gas permeation amount required for preserving thefreshness of fruits and vegetables in a modified atmosphere. If thecontent of the container is frozen cooked food, the hot needles of thesealing machine can be restrained from operation; alternatively, themelted holes formed by the hot needles are located in an area coveredwith the airtight sealing strip. Thus, a totally air tight food packageis formed, with the airtight sealing strip covering theline-segment-shaped, spaced slits, so as to prevent ice burn which mayotherwise occur after a long-term frozen storage period. This air tightstructure is also suitable for low vacuum packaging or inert gas purgingpackaging. When food packaged in a container of this structure is heatedby microwave, the huge amount of hot steam generated instantaneously isregulated by the plurality of line-segment-shaped, spaced slits, therebyprotecting the container from bursting. Meanwhile, water and otherliquids in the food are largely preserved during microwave heating andprevented from splashing in the microwave oven, thus reducing the timeand water resource required for cleaning the microwave oven.

More importantly, this packaging material provides a reversible andautomatic air permeation and pressure regulation function. Beforemicrowave heating, the packaging material has a closed structure. Duringheating, the packaging material automatically regulates steam pressureso as for food in the container to undergo a continuously pressurizedheating process while the container and the packaging material areprotected from bursting. When cooled after microwave heating is stopped,the packaging material substantially resumes its closed structure. Thispressure- and temperature-dependent reversible structure is reusable andreheatable, which is a far cry from the conventional food-packagingmaterials which must be pulled or cut open to the packaging materialbefore microwave heating.

The inventor of the present invention has also granted several patentsfor the core techniques of microwavable food-packaging film materials.The disclosed packaging film can be further integrated and benefit thepresent invention. These patents include Japanese Patent No. 3747004;U.S. Pat. Nos. 7,077,923 and 7,208,215; Korean Patent No. 0536896;Canadian Patent No. 2381146; and Australian Patent No. 780966. Thepresent invention further integrates the mechanical hardware of asealing machine with a lidding film so as for food packager to provide amore flexible packaging option which selectively combines microwaveableand the ability to preserve freshness according to product needs.

As mentioned above, the present invention provides a sealing machine forrendering a food container capable of modified-atmosphere freshnesspreservation as well as automatic pressure regulation to the build upvast hot steam during microwave heating. A container that can be as itis heat-sealed by the sealing machine is made of a material selectedfrom plastic, wood, paper, synthetic paper, and ceramic, or acombination thereof. Each of the lidding film and the sealing stripincludes at least one layer of stretched film and is made of a materialselected from the group consisting of polyolefin, polyester,polypropylene (PP), polyethylene (PE), polystyrene (PS), polyvinylchloride (PVC), polycarbonate (PC), polyamide, nylon, polyethyleneterephthalate (PET), polyvinyl alcohol (PVA), ethylene-vinyl acetate(EVA), ethylene vinyl alcohol (EVOH), polyvinyl dichloride (PVDC),ethylene-styrene copolymer (ES), wax paper, synthetic paper, glassinepaper, polymer-coated paper, paper, and a combination thereof.

The primary objective of the present invention is to provide a sealingmachine for sealing an opening of a container containing frozen orrefrigerated food. The sealing machine includes a lidding-filmprocessing unit, a bonding unit for bonding an airtight sealing strip toa lidding film, and a heat-sealing unit for covering the opening of thecontainer with the lidding film. In the lidding-film processing unit,the lidding film is unwound and extended downward from a roll stock ofthe lidding film so as to pass over a table. Die cutters and hot needlesprovided at the table move back and forth vertically to formline-segment-shaped, spaced slits and dot-shaped atmosphere-modifyingbreathing holes at predetermined positions on a surface of the liddingfilm. The processed lidding film proceeds to the bonding unit, in whicha roll of airtight sealing strip located above a table is unwound,extended downward, and laid over the lidding film passing through thebonding unit. Thus, the line-segment-shaped, spaced slits formed on thelidding film are covered by the airtight sealing strip. Then, theairtight sealing strip, whose bottom is provided with adhesive, isbonded to the lidding film by means of a hot-press sealing assemblyinstalled at the table of the bonding unit. Afterward, the lidding filmboned with the airtight sealing strip enters the sealing unit configuredfor sealing an opening of a container. In the sealing unit, a containercontaining frozen or refrigerated food is in place in a supporting frameof a table. The lidding film passes over the supporting frame and thuscovers the container. A heat-sealing assembly provided at the table ofthe heat-sealing unit seals the lidding film covering the container to aheat-sealable flange along the rim of the opening of the container.Scraps of the used lidding film are cut adjacent to the rim of theopening of the container and wound up around a rewinding spool. Thus,the lidding film which is now covering the container has been processedand sealed to the container in a continuous manner to effectivelysimplify sealing of the container and removal of the scraps cut from theused lidding film.

According to the present invention, the dot-shaped atmosphere-modifyingbreathing holes formed by being melted through by the hot needles mayvary in size, depending on the diameter and vertical insertion depth ofthe slender and pointed hot alloy needles which are resistant to hightemperature and each have a round sectional shape. When cooled, themelted breathing holes have fixed shapes and will not close. Thus, thebreathing holes form an open structure having a slight but quantifiableair-permeation capacity. To achieve a desired air-permeation capacity,the number and size of the breathing holes are determined by the kindsand total weight of fresh fruits and vegetables to be packaged in thecontainer, as well as by the temperature and duration of storage andtransportation. The diameter and air-permeation capacity of thebreathing holes are quantitatively tested by a digital opticalmicroscope and an air permeation testing machine, respectively. Thediameter of the melted dot-shaped breathing holes ranges from 0.1 mm to1.5 mm.

If the hot needles in the sealing machine of the present invention arenot actuated, the resultant sealed food container is completely closed.The original oxygen-containing air in the container can be replaced by agas mixture including a preset percentage of inert gas such as nitrogenand carbon dioxide. Alternatively, the completely air tight foodcontainer is processed by vacuum packaging or other food packagingtechniques. Nevertheless, during microwave cooking, build uphigh-temperature, high-pressure hot steam generated from within thepackaged food can be regulated via the line-segment-shaped, spaced slitson the lidding film so as to prevent the container and the lidding filmfrom bursting.

For operational safety, the sealing machine of the present invention isadditionally provided with a protection shield outside and around thedie cutters and hot needles of the lidding-film processing unit, therebypreventing an operator from being injured during operation. Anothersafety feature of the sealing machine of the present invention is aprotection shield outside and around the hot-press sealing assembly ofthe bonding unit such that the operator's hands are protected from beingsqueezed.

Presented below is an example of applying the present invention tofresh-cut produce or, more specifically, to Babylon which was freshlypicked, washed, cut, centrifugally dried, and vacuum pre-cooled. The 342gm Babylon was placed in microwavable polypropylene (PP) trays eachhaving dimensions of 140 mm×200 mm×50 mm (W×L×H). A laminated PET/PPlidding film, 220 mm in width, was unwound from a spool and processed bythe die cutters and the hot needles so as to have a row of equallyspaced slits shaped as 7-mm line segments and a row of dot-shapedatmosphere-modifying breathing holes, wherein the two rows are parallelto each other and offset by 3 cm. The lidding film has eight 7-mmline-segment-shaped, spaced slits and ten dot-shapedatmosphere-modifying breathing holes in an area above each fresh-cutproduce loaded tray, wherein each melted breathing hole has a diameterof 0.15 mm. The row of line-segment-shaped, equally spaced slits wasthen covered by and bonded within a 20-mm wide, airtight sealing strip.Finally, the lidding film bonded with the airtight sealing strip wassealed, by the heat-sealing unit, to a rim of the opening of eachfresh-cut produce loaded tray. As a result, only the ten 0.15-mmdot-shaped atmosphere-modifying breathing holes were exposed on thelidding film of each tray to provide modified-atmosphere freshnesspackaging condition. After being refrigerated at a constant temperatureof 5° C. for two weeks, the Babylon did not yellow, was free of mold,and did not produce unpleasant odor. When subsequently cooked in a1100-watt microwave oven full power for five minutes, the large amountof build up hot pressurized steam generated intray during the heatingprocess was automatically regulated via the eight 7-mmline-segment-shaped, spaced slits under the 20-mm wide, airtight sealingstrip such that neither the lidding film nor the tray burst.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention as well as a preferred mode of use, further objectives,and advantages thereof will be best understood by referring to thefollowing detailed description of an illustrative embodiment inconjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic drawing showing the operating procedure of asealing machine according to the present invention;

FIG. 2 is a top view of a lidding film bonded with an airtight sealingstrip according to the present invention;

FIG. 3 is a perspective view of the lidding film and a container yet tobe sealed by the lidding film;

FIG. 4 is perspective view of the container sealed by the lidding film;and

FIG. 5 is a perspective view showing the airtight sealing strip beingpeeled off from the lidding film.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a sealing machine for sealing a foodcontainer and thus rendering the food container capable of keepingfruits and vegetables fresh in a modified atmosphere and automaticallyadjusting pressure generated during microwave heating. Referring to FIG.1 and FIG. 5, a sealing machine 4 according to the present invention isconfigured to seal a heat-sealable rim of an opening of a container 7containing frozen or refrigerated food. The sealing machine 4 includes alidding-film processing unit 1, a bonding unit 2 for bonding an airtightsealing strip 6 to a lidding film 5, and a heat-sealing unit 3 forcovering the opening of the container 7 with the lidding film 5.

In the lidding-film processing unit 1 shown in FIG. 1, the lidding film5 is reeled out and extended downward to a table 12 from a roll of thelidding film 5 that is wound around a spool 11. A perforating assembly13 at the table 12 moves back and forth vertically to effectuatecutting. The perforating assembly 13 includes die cutters 131 and hotneedles 132 and is operable in different ways according to the food tobe packaged. For instance, if the packaged food only requiresmodified-atmosphere freshness packaging, the hot needles 132 of theperforating assembly 13 are actuated to melt through the lidding filmand thus form dot-shaped atmosphere-modifying breathing holes 53 atpredetermined positions on a surface of the lidding film 5 while thelidding film 5 passes through the lidding-film processing unit 1. If thepackaged food only requires microwave cooking, the die cutters 131 ofthe perforating assembly 13 are actuated to form line-segment-shapedspaced slits 52 at predetermined positions on the surface of the liddingfilm 5 while the lidding film 5 passes through the lidding-filmprocessing unit 1. If the packaged food needs modified-atmospherefreshness preservation as well as microwave cooking, both the diecutters 131 and the hot needles 132 of the perforating assembly 13 areactuated to form the desired line-segment-shaped, spaced slits 52 anddot-shaped atmosphere-modifying breathing holes 53 at predeterminedpositions on the surface of the lidding film 5, as shown in FIG. 2,while the lidding film 5 passes through the lidding-film processing unit1. An additional protection shield 15 is provided outside and coveredthe perforating assembly 13 of the lidding-film processing unit 1 toprevent an operator's hands from being operational injury by accident.

As shown in FIG. 1, the processed lidding film 5 moves on to the bondingunit 2, in which a roll stock of an airtight sealing strip 6 is reeledout downward from a spool 21 above a table 22 and is laid over thelidding film 5 that passes through the bonding unit 2. Thus, referringto FIG. 2, the airtight sealing strip 6 covers the line-segment-shaped,spaced slits 52 formed on the lidding film 5. The airtight sealing strip6, which has a bottom side provided with adhesive layer material, isbonded to the lidding film 5 by a hot-press sealing assembly 23installed at the table 22. A protection shield 24 is additionallyprovided outside and around the hot-press sealing assembly 23 of thebonding unit 2 to protect the operator's limbs from being squeezed andinjured.

Afterward, referring back to FIG. 1, the lidding film 5 bonded with theairtight sealing strip 6 advances to the heat-sealing unit 3, which isconfigured to seal the rim of the opening of the container 7 after thecontainer 7 is filled with food. The container 7 containing frozen orrefrigerated food is in place in a supporting frame 32 of a table 31 soas to be covered by the passing lidding film 5, as shown in FIG. 3. Thelidding film 5 covering the container 7 is then sealed to aheat-sealable rim 72 of an opening 71 of the container 7, as shown inFIG. 4, by means of a heat-sealing assembly 33 installed at the table31. Scraps 54 outside the new heat-sealed rim 72 of the container 7 arecut from the lidding film 5 and reeled in by a rewinding spool 34located at an opposite end of the heat-sealing unit 3, as shown in FIG.1.

Thus, the lidding film 5 shown in FIG. 5 as covering the opening 71 ofthe container 7 has been die cut, punctured, sealed airtight,heat-sealed to the rim 72 of the container 7, and rid of the scraps 54in a continuous manner. In consequence, the sealing of the container 7and removal of the scraps 54 are effectively simplified.

While the present invention is described herein by reference to apreferred embodiment, it is understood that the embodiment is notintended to limit the scope of the present invention. A person skilledin the art can make various changes or modifications to the disclosedembodiment without departing from the concept and scope of the presentinvention. Therefore, the scope of the present invention is defined onlyby the appended claims.

1. A sealing machine for a fresh-keeping and cooking container, the sealing machine comprising a lidding-film processing unit, a bonding unit for bonding an airtight sealing strip to a lidding film, and a heat-sealing unit for covering an opening of the container with the lidding film; wherein, in the lidding-film processing unit, the lidding film is unwound and extended downward to a table from a roll of the lidding film, and a perforating assembly at the table is actuated to form line-segment-shaped, spaced slits or dot-shaped atmosphere-modifying breathing holes at predetermined positions on a surface of the lidding film passing through the lidding-film processing unit; wherein, as the processed lidding film enters the bonding unit, the airtight sealing strip is unwound and extended downward from a roll of the airtight sealing strip above a table of the bonding unit and is laid over the lidding film passing through the bonding unit such that the line-segment-shaped, spaced slits formed on the lidding film are covered, the airtight sealing strip, whose bottom is provided with adhesive, being bonded to the lidding film via a hot-press sealing assembly at the table of the bonding unit; wherein, as the lidding film bonded with the airtight sealing strip enters the heat-sealing unit configured for sealing the opening of the container, the container, which contains frozen or refrigerated food and is placed in a supporting frame of a table of the heat-sealing unit, is covered by the lidding film passing through the heat-sealing unit, and the lidding film covering the container is sealed to a heat-sealable rim of the opening of the container via a heat-sealing assembly at the table of the heat-sealing unit while scraps cut from the used lidding film are wound around a rewinding spool at an opposite end of the heat-sealing unit; and wherein the lidding film covering the opening of the container is processed and sealed to the container in a continuous manner to effectively simplify sealing of the container and removal of the scraps cut from the used lidding film.
 2. The sealing machine of claim 1, wherein the perforating assembly of the lidding-film processing unit comprises hot needles.
 3. The sealing machine of claim 1, wherein the perforating assembly of the lidding-film processing unit comprises die cutters configured for forming the line-segment-shaped, spaced slits.
 4. The sealing machine of claim 1, wherein the perforating assembly of the lidding-film processing unit comprises hot needles and die cutters configured for forming the line-segment-shaped, spaced slits.
 5. The sealing machine of claim 1, wherein a protection shield is provided outside and around the perforating assembly of the lidding-film processing unit.
 6. The sealing machine of claim 1, wherein a protection shield is provided outside and around the hot-press sealing assembly of the bonding unit of the sealing machine. 